Two-Layer XBAR Electrodes for 5G Spurious Mode Reduction
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Solution Overview
Problem
Existing RF filters using acoustic wave resonators are not well-suited for higher frequency communications bands, such as those defined in the 5G NR standard, particularly in bands n77 and n79, due to limitations in power handling and spurious mode reduction.
Innovation Solution
The development of transversely-excited film bulk acoustic resonators (XBARs) with optimized IDT finger geometries, including pedestal-like and wedding cake-like cross-sectional shapes, to enhance power handling and reduce spurious modes, thereby improving filter performance at higher frequencies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If conventional IDT finger geometries are used in acoustic wave resonators, then the device structure is simple and easy to manufacture, but power handling capability is insufficient and spurious modes are not effectively reduced for higher frequency bands
Solution Approach 1:
The IDT finger structure is segmented into multiple distinct geometric regions including a narrower top layer and a wider bottom layer, creating a composite cross-sectional shape that optimizes both power handling and spurious mode reduction while maintaining manufacturability through defined segmentation zones
Solution Approach 2:
The IDT finger geometry employs asymmetric cross-sectional shapes where the top layer width differs from the bottom layer width, creating pedestal-like or wedding cake-like structures that improve power handling capability and reduce spurious modes in higher frequency 5G bands
2Reliability
If existing RF filter designs are used, then manufacturing processes are established and cost-effective, but performance in higher frequency communications bands (5G n77, n79) is inadequate
Solution Approach 1:
Different regions of the IDT finger structure are assigned different geometric qualities - the top layer has a narrower width for improved high-frequency performance while the bottom layer has a wider width for enhanced power handling, with each region optimized for its specific functional requirement
Solution Approach 2:
The solution transitions from conventional two-dimensional IDT finger cross-sections to three-dimensional composite structures with varying width profiles, introducing vertical dimensionality changes that create pedestal-like or wedding cake-like geometries for improved 5G band performance
3Ease of manufacture
If broader IDT finger top layers are used, then manufacturing is easier, but spurious modes are not effectively reduced
Solution Approach 1:
The IDT finger is segmented into top and bottom layers with different width characteristics, allowing the top layer to be narrower for spurious mode reduction while the bottom layer provides a broader base for manufacturability, with the segmentation enabling both goals to be achieved simultaneously
Solution Approach 2:
The geometric parameters of the IDT finger are changed by defining different width values for the top layer versus the bottom layer, creating a composite cross-sectional shape that reduces spurious modes through the narrower top portion while maintaining ease of manufacture through the wider bottom portion
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The use of XBARs with optimized IDT finger geometries effectively addresses the challenges of power handling and spurious mode reduction, enabling the creation of high-performance RF filters capable of operating in the higher frequency bands defined for 5G communications.
Implementation Method 1
an interdigital transducer (IDT) formed on the piezoelectric plate
Implementation Method 2
transversely-excited film bulk acoustic resonators (XBARs) with optimized IDT finger geometries
Data Source
AI summary
A bulk acoustic resonator is provided that includes a piezoelectric layer, and an interdigital transducer on a surface of the piezoelectric layer and including a plurality of interleaved fingers. At least one finger of the plurality of interleaved fingers comprises a first layer having a bottom surface that contacts the surface of the piezoelectric layer. The at least one finger includes a second layer having a bottom surface that contacts a top surface of the first layer. Moreover, a width of the bottom surface of the second layer is less than a width of the bottom surface of the first layer.